This 1975 transmission electron micrograph (TEM) revealed the presence of a number of infectious bronchitis virus (IBV) virions, which are Coronaviridae family members, and members of the genus Coronavirus. IBV is a highly contagious pathogen, which infects poultry of all ages, affecting a number of organ systems including the respiratory and urogenital organs. IBV is categorized as a Group 3 coronavirus member, with a helical genome composed of positive-sense single-stranded RNA ((+) ssRNA). This is an enveloped virus, which means that its outermost covering is derived from the host cell membrane.

The coronavirus derives its name from the fact that under electron microscopic examination, each virion is surrounded by a “corona” or halo. This is due to the presence of viral spike peplomers emanating from its proteinaceous capsid. One of the most infamous of the coronaviruses is the SARS-CoV, the cause of severe acute respiratory syndrome (SARS).